Accessory cell processing of foreign antigen is central to the initiation of all immune responses. Under different experimental circumstances a variety of cell types have been shown to be able to perform a number of accessory functions. This study will compare the ability of circulating bone marrow derived (monocytes, dendritic cells and EBV transformed B cells) and mesenchymal (endothelial and smooth muscle cells) from the same human donor to present influenza virus and tetanus toxoid antigens to autologous T cell clones. Class II MHC antigen positive allogeneic IFN-Gamma treated mesenchymal cells can elicit alloproliferative responses and that IFN-Gamma treated fibroblasts can present tetanus toxoid to autologous T cell clones. It is our hypothesis that endothelial cells and smooth muscle cells are critical for routine antigen specific lymphocyte trafficking, delayed hypersensitivity and graft rejection in vivo, as these cells are in intimate contct with circulating thymus derived lymphocytes. Specific aims include 1) generation of antigen specific T cell clones and mesenchymal cells from patients undergoing coronary artery bypass surgery, 2) establishment of longterm EBV transformed B cell lines from the same patients, 3) the characterization of clones for phenotype, specificity of class II antigen restriction and fine specificity of viral antigen response, 4) the ability of clones to reespond to IFN-Gamma treated mesenchymal cells in the presence of antigen, 5) evaluation of virus specific clones for cytolytic activity, 6) comparison of bulk populations of peripheral T cells form the same donors with the clones for the ability to respond to accessory cells of different cell types and 7) analysis of the role of T cell accessory molecule (i.e. LFA, CD4) in responses with different antigen presenting cells using monoclonal antibody blocking of proliferative responses. Techniques used in these studies are cell separation, cell culture, limit dilution cloning, B cell transformation, fluorescence activated cell sorting, proliferation and cytolytic T lymphocyte assays.